EE Times Under The Hood - October 8, 2007 - (Page 24) under the hood: MOBILE months to sort out. But when we were done, we had something to work towards.” PSoC is a mixed-signal array with programmable logic. Hence, it can be configured for various functions, including capacitive sensing. Cypress set out with a goal of creating a firmware platform that could be easily changed. This is done with “user modules,” which are preconfigured analog and digital blocks that handle a specific function. For example, the digital blocks become an 8- or 16-bit pulse width modulator, and an analog and a digital block can combine to form a digital-to-analog converter. The blocks can be programmed to be communications interfaces, such as a SPI or half- and fullduplex UARTs. The capacitive sensing was handled in such a user module, which includes all the sensing, the baseline update and the decision processes. “At the same time we were working on the LG project, we were working on the CapSense user module,” says Virge. “We were careful to put in all the requirements that LG would need to be able to do the application correctly into the user module. That same user module, and all the reference code that goes with it, has since been used in a few LG handsets.” The intellectual property with the www.eetimes.com • www.techonline.com The handset’s user module includes all the sensing, the baseline update and the decision processes. user modules belongs to LG. Hence, they can make changes themselves and own those changes, making the module fit their specific needs. In the case of LG, they’ve actually used a modified version of this user module within other parts of the company, such as the group developing white goods. The Cypress IC in this handset is the CY8C21434-24LFXI, housed in a 32-pin, 5- by 5-mm package. The sensor itself consists of nine copper pads on the opposite side of the board from the IC. Each pad has a hole in it where the light from the LED shines through. Each pad is connected to a PSoC I/O. Because the PSoC is actually a microcontroller, it has the ability to perform other functions besides the CapSense. In the case of the Chocolate, LG integrated the LED drivers. Because of where the IC is located on the board, it became an obvious choice to integrate that control, or anything else related to the sensor. One such function is the Component focus While resistive touch sensors have been popular for many applications due to their simplicity and availability, their reliability issues and tendency to impair the underlying optics have spurred makers of mobile devices to find an alternative. Enter capacitive sensors, which circumvent both issues while providing a cleaner interface. Recognizing this, Cypress introduced its CapSense technology in May 2005. Based on its PSoC mixed-signal arrays, CapSense can replace dozens of mechanical switches and controls with relatively simple, touch-sensitive controls to allow a designer to incorporate multiple capacitive sensing design elements into an application. Buttons, sliders, touchpads, touchscreens and proximity detectors are supported simultaneously with the same device in the same circuit. For more on capacitive sensing, go to www.mobilehandsetdesignline.com and search article ID: 196603071. For more on CapSense, go to http://portal.cypress.com/capsense. ability to look for the priority of a button press. In other words, at different times, you want certain buttons to be easier to press than others, based on the button press that preceded it. This is helpful when it appears that two buttons are pressed at the same time, possibly because the user has a big finger. As a result, the PSoC has a good chance to determine which button the user intended to press. LG’s designers were also concerned with electrostatic discharge (ESD) protection. Meeting the needs of the ESD requirements with the changing electrical and mechanical designs of each new model can be a challenge. When an ESD event occurs on the sensor, it impacts the integrity of the received data. The way to circumvent a negative impact is with algorithms that can differentiate between an ESD event and a valid button press. Hence, it must recognize and ignore the ESD event, which tends to have a fairly specific signature when compared with data. The PSoC waits for a few cycles then checks the sensor again. Another LG design change that had to be accommodated was a move from an FR4 board to a flex pcb. FR4 is thicker, which is a little easier to design with because you can better distance the signals from a ground plane on the back side of the board. The result is less native capacitance, therefore higher proportional change. FR4 also costs less. The flex pcb gives the system designers more mechanical options, which were needed on this tight design. Like many of the CDMA handsets I take apart, this one contains lots of Qualcomm ICs. The Chocolate is built with an MSM6500 baseband, an RFT6150 transceiver, and an RFR6500 receive diversity device. Some of the other identifiable components include a Wolfson 8973G audio equalizer, a Toshiba multichip package memory device, and a Maxim power-management controller. ■ 24 Electronic Engineering Times, TechOnline | October 8, 2007 http://www.eetimes.com http://www.techonline.com http://www.mobilehandsetdesignline.com http://portal.cypress.com/capsense
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.